The principle behind electro-magnetic (EM) tracking is that a field generator produces spatially varying magnetic fields which induce currents in sensor coils. A measurement system is then used to calculate the position and orientation of the sensors, based on measured voltages in the sensors. EM tracking techniques provide real-time position and orientation information in 3D space, which may be used to aid interventional procedures. Since the size of these sensor coils is very small, they can be embedded into a catheter or other surgical tool and be used for guided navigation. As a result, EM tracking systems are very well suited to in-body interventions.
When electromagnetic tracking is used in conjunction with x-ray imaging, such as in a cathlab, the electromagnetic (EM) tracking field generators can corrupt the x-ray images, particularly rotational images from a cone beam CT scan. Even though efforts have been made to design x-ray compatible field generators that do not show any large electronic components in the x-ray image, there are still features that can produce artifacts that are visible on the x-ray image. These features include wires that run from the top to the bottom of the field generator and sharp edges of the outer and inner casings of the field generator. These features typically cause artifacts in the shape of lines on the x-ray image.